1. Field of the Invention
This invention relates to a control system for internal combustion engines, for calculating a rate of variation in combustion based on the state of combustion of the engine, and adjusting control parameters such that the calculated rate of variation in combustion becomes equal to desired values dependent upon operating conditions of the engine.
2. Prior Art
Conventionally, a control system of this kind has been proposed by Japanese Laid-Open Patent Publication (Kokai) No. 5-1614, which calculates a rate of variation in combustion based on the state of combustion of an internal combustion engine, and adjusts control parameters such that the calculated rate of variation in combustion becomes equal to desired values dependent upon operating conditions of the engine, to thereby meet two rather contradictory kinds of demand: improved drivability (reduction in sensed vehicle vibrations) and reduced fuel consumption and improved exhaust emission characteristics. According to the proposed control system, the shift position of a transmission connected to the engine is detected, and one of desired torque variation maps set in advance is selected according to the detected shift position to determine a desired torque variation from the selected map. The desired torque variation, which is thus corrected according to the shift position, is set to a rather low value at or in the vicinity of a vehicle speed resonance point.
Vibrations of the engine transmitted to the vehicle chassis (vibrations sensed by the driver) also vary in dependence on a degree of absorption of the vibrations by the driving system of the vehicle. The degree of absorption of the vibrations by the driving system depends not only on the shift position of the transmission but also on the state of engagement of a lock-up clutch provided in the transmission and a slip ratio of a torque converter also provided in the transmission. Therefore, the proposed control system cannot fully meet the two kinds of demand: improved drivability (reduction in sensed vehicle vibrations) and reduced fuel consumption and improved exhaust emission characteristics.